Ive had my s2k for a while and I used to get 26ish mpg's. I am in no way nice to it and figured that was normal enough for my driving style. however, I put a mugen wing on it and at about that same time my mileage dropped to 20. I assumed it was because the mugen was adding lots of drag and caused my mileage to drop.

2 months ago, I sold the mugen and was expecting my mileage to start increasing, only it didnt. Im still struggling To get more than 200 miles out of a tank. the funny part is, I can rev the piss out of it and get 200 miles or drive it gently and get 215 miles.

whats going on?

plugs were replaced though not with oe spec ones, stock airbox w/ k&n, 63mm testpipe, map/iacv thoroughly cleaned, and 174k miles-no codes whatsoever. Im thinking about changing the front o2 sensor, but im unemployed and simply cant start throwing money at a problem without a clear cause. I do need to do a valve adjustment

 

Out of spec valves will effect fuel economy.

 

plug in a scanner. maybe an o2 sensor is going out. mainly the primary. other things to consider as well would be, alignment and tire pressure.

 

That's a pretty drastic drop though...

 

ive scanned it several times, absolutely no codes- and car screams like a banshee. im wondering if the brakes could be dragging or the like

 

possibility for the brakes as well. could be the plugs? were they gaped properly? also i read somewhere that gas formulas are different for summer and winter. could possible cause the drop as well.

 

You should hear some noise from the valves, unless they have been adjusted recently. Check tire pressure as well.

 

Weather? Depending upon driving cold temps can drop mileage as much as 10%.

 

Several things here to check that are free, just your time.

- valve adjust
- brake drag
- tire pressure
- plug gap

Try all those first. Also the winter gas thing, its a double wammy, because cold weather also lower mileage, then winter gas on top of that. So that could also be contributing.

Report back after ruling out all above.